Bash script to fix internet access in WSL2 via powershell when connected to VPN which changes network interface adapter (like Cisco AnyConnect)

wsl-vpn-net-fix.sh

#!/bin/bash

# MIT License
# -----------------------------------------------------------------------------
# Copyright 2022 Sourabh Verma

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is furnished
# to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
# INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
# PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
# -----------------------------------------------------------------------------

TMP=`mktemp`
trap ctrlC INT

removeTempFiles() {
	rm -f $TMP
}

ctrlC() {
	echo
	echo "Trapped Ctrl-C, removing temporary files"
	removeTempFiles
	stty sane
}

WUSR=$(powershell.exe whoami | powershell.exe whoami | cut -f2- -d '\' | sed 's/\r$//')

P1="/mnt/c/users/$WUSR/pwsh/netfix.ps1"
P2="/mnt/c/users/$WUSR/pwsh/cisconetfix.ps1"
WP1="C:\Users\\$WUSR\pwsh\netfix.ps1"
WP2="C:\Users\\$WUSR\pwsh\cisconetfix.ps1"

C1="start-process powershell -verb runas -ArgumentList '-F \"$WP2\"'"
C2="Get-NetAdapter | Where-Object {\$_.InterfaceDescription -Match \"Cisco AnyConnect\"} | Set-NetIPInterface -InterfaceMetric 4000"
C3="Get-NetIPInterface -InterfaceAlias \"vEthernet (WSL)\" | Set-NetIPInterface -InterfaceMetric 1"


if [ ! -f "$P1" ]; then
	echo "$P1 does not exist. Creating..."
	mkdir -p "$(dirname "$P1")"
	echo $C1 > "$P1"
fi

if [ ! -f "$P2" ]; then
	echo "$P2 does not exist. Creating..."
	mkdir -p "$(dirname "$P2")"
	echo $C2 > "$P2"
	echo $C3 >> "$P2"
fi

echo 'Mapping new network interfaces.'
echo '-------------------------------'
echo '(Enter your credentials in UAC Prompt)'
echo
echo

powershell.exe -File "$WP1"

echo "Current resolv.conf"
echo "-------------------"
cat /etc/resolv.conf

echo
echo "Creating new resolv.conf"
echo "------------------------"

{
	head -1 /etc/resolv.conf | grep '^#.*generated'
	for i in `powershell.exe -Command "Get-DnsClientServerAddress -AddressFamily ipv4 | Select-Object -ExpandProperty ServerAddresses"`; do
		echo nameserver $i
	done
	tail -n+2 /etc/resolv.conf | grep -v '^nameserver'
} | tr -d '\r' | tee $TMP

(set -x; sudo mv $TMP /etc/resolv.conf)